The present invention relates to a seat belt control device and method, particularly of the kind that can dispense with a conventional seat belt locking mechanism by controlling a DC motor suitably thereby making a seat belt system smaller in size.
A seat belt system for vehicles is constructed so as to apply a tension to a seat belt by means of a seat belt retractor. In use of the seat belt system, a passenger pulls out a seat belt that is anchored to a vehicle body by two anchors and one through-anchor and engage a portion of the seat belt with a buckle fixed to a seat. Thereafter, when the passenger loosens his/her hold of the seat belt, the seat belt retractor retracts the slackened seat belt by the action of a spring and applies to the seat belt a tension that is determined by the spring thereby restraining the passenger in a seat.
Such a spring type seat belt system has a problem that it is necessary for the passenger to pull out the seat belt from the seat belt retractor against the bias of the spring and the seat belt system is unstable in operation since it utilizes the resilience of the spring.
To solve such a problem, it has been proposed a technique that realizes a seat belt system that is flexible in operation by using a DC motor for its seat belt drive section and controlling the rotational direction and speed of the DC motor as disclosed in Japanese Patent Provisional Publication No. 2000-318574.
With the seat belt system in which the DC motor is used in a seat belt retractor in place of a spring, it is necessary to lock the seat belt upon collision by means of a locking mechanism that is provided separately from the seat belt retractor.
However, the seat belt system with the seat belt retractor using the DC motor is larger in size as compared with a seat belt system with a seat belt retractor using a spring.
It is accordingly an object of the present invention to provide a seat belt control device that can dispense with a conventional seat belt locking mechanism by suitably controlling a DC motor and can make a seat belt system smaller in size.
To accomplish the above object, there is provided according to an aspect of the present invention, a seat belt control device comprising a drive motor connected to a seat belt for winding and unwinding the seat belt, a controller for controlling the drive motor, a wearing state sensor for detecting a wearing state of the seat belt, a vehicle speed sensor for detecting a vehicle speed, and a deceleration sensor for detecting deceleration of a vehicle, wherein the controller shorts electrodes of the drive motor when the seat belt is worn, the vehicle speed is higher than a first predetermined vehicle speed value, and an absolute value of the deceleration of the vehicle is lower than an absolute value of a first predetermined deceleration value.
There is provided according to another aspect of the present invention a seat belt control method comprising detecting a wearing state of the seat belt, detecting a vehicle speed, detecting deceleration of a vehicle, and controlling a drive motor for winding and unwinding a seat belt based on the wearing state of the seat belt, the vehicle speed and the deceleration of the vehicle, wherein the controlling comprises shorting electrodes of the drive motor when the seat belt is worn by a passenger, the vehicle speed is higher than a first predetermined vehicle speed value, and an absolute value of the deceleration of the vehicle is lower than an absolute value of a first predetermined deceleration value.